In the western world diabetes mellitus is one of the most common severe diseases in childhood, but it is rarely seen in black African populations. However, there are very few epidemiological studies of childhood diabetes in Africa and almost nothing is known of the Nigerian population. One aim of this study was therefore to estimate the prevalence of insulin dependent diabetes (IDDM) in children and adolescents and to characterize their type of diabetes.A screening of almost 78,000 school children was performed and beside some already known diabetic patients several new cases were diagnosed. It was found that IDDM is much less common than in Europe but on the other hand more common than in several Asian countries. In addition the prevalence found may be underestimated because of cultural and social factors, health care problems and high mortality in diabetes. Although most patients had a clinical picture of Malnutrition Related Diabetes (MRD) we found in some cases autoantibodies towards islet cells and insulin and furthermore the same HLA-DQ-type-associations as seen to Type 1 diabetes in caucasian diabetics.While we saw no seasonal variation of diagnosis of Nigerian IDDM, there is a pronounced such seasonal variation in Sweden. This study has tried to elucidate whether this seasonal variation is related to any differences in manifestation and clinical course. Patients diagnosed during incidence peaks had more often short duration of symptoms before diagnosis,ketonuria at diagnosis, rapid loss of endogenous insulin secretion but increase of insulin antibodies and of glycosylated haemoglobin. They had also more often infections before diagnosis and high serum immunoglobulins (IgG and IgM) up to 9 months after diagnosis. HLA-DR4 was more common in these patients. The results suggest that IDDM in Swedish children is heterogenous.